In recent years, manufacturing technology of liquid crystal display panels using thin film transistors (TFT) has been advancing, and upsizing of the panel and the display unit screen is going on. This manufacturing technology is applied to a large-area sensor having a conversion element (photoelectric conversion element) including a semiconductor and a switching element such as the TFT. Such an area sensor (radiation imaging sensor panel) is combined with a scintillator that converts radiation into light, e.g., visible light, and is used in the field of radiation imaging apparatus such as a medical X-ray imaging apparatus.
Heretofore, an imaging method used by medical image diagnosis has been roughly classified into plain radiography for obtaining a still image and fluoroscopic radiography for obtaining a moving image. However, for the moment, the above-described radiation imaging apparatus begins to be used mainly for plain radiography. At the same time, the situation is such that the reading speed is not sufficient for fluoroscopic radiography.
Hence, in U.S. Patent Application Publication 2005/145800 (Japanese Patent Application Laid-Open No. 2003-218339), one pixel of the area sensor includes the conversion element, a transfer switch (transfer TFT and the like) for transferring a signal from the conversion element, and a reset switch (reset TFT) for resetting the conversion element. This configuration provides a radiation imaging apparatus having a faster reading speed.
In general, the structure of the pixel of the area sensor (radiation imaging sensor panel) is roughly classified into two types, a flat type, which has the conversion element and the switching element on the same flat surface, and a lamination type, which has the conversion element over the upper side of the switching element. The former can simplify the manufacturing process since the conversion element and the switching element can be formed by the same semiconductor manufacturing process. The latter type can form the area of the conversion element larger in one pixel as compared to the flat type since the conversion element is disposed over the switching element. Therefore, an aperture ratio of the pixel can be made large, so that the pixel becomes highly sensitive. For this reason, in Patent Document 1, the lamination type sensor is also described.
FIG. 11 is a plan view of the radiation imaging apparatus using a conventional lamination type structure. Although in fact a scintillator is disposed over the pixel of the radiation imaging apparatus, it is omitted from FIG. 11.
The conventional radiation imaging apparatus includes, within one pixel as shown in FIG. 11, a conversion element (photoelectric conversion element) 101, a transfer switch (transfer TFT) 102, and a reset switch (reset TFT) 103.
An under-electrode of the conversion element and a source or drain electrode of the transfer switch are connected through a contact hole. Similarly, the under-electrode of the conversion element and the source or drain electrode of the reset switch are also connected through a contact hole. Hence, a contact hole is provided for each switching element.